to know sth because of sth unpleasant that has happened to you :
He's a ruthless businessman, as I know to my cost.
to know sth because of sth unpleasant that has happened to you :
He's a ruthless businessman, as I know to my cost.
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005